In recent years, in OFDM (Orthogonal Frequency Division Multiplexing) scheme, studies are conducted for a technique of employing adaptive modulation and frequency scheduling in each RB (Resource Block) grouping a plurality of subcarriers, and improving spectrum efficiency. Adaptive modulation refers to a scheme for deciding coding rates and modulation schemes according to channel conditions observed on the receiving side so that a predetermined packet error rate is satisfied. With frequency scheduling, a plurality of mobile stations report channel conditions observed per RB on the receiving side, and the base station collects the channel conditions and allocates RBs to mobile stations according to a predetermined scheduling algorithm. Values used in these adaptive modulation and frequency scheduling for reporting channel conditions are called channel quality information (CQI: Channel Quality Indicator).
As for CQI, parameters showing channel quality of contiguous RBs corresponding to the minimum unit of frequency scheduling are a “narrowband CQI,” that is, a subband CQI, and parameters showing channel quality of overall system bandwidth are a “wideband CQI,” that is, a system bandwidth CQI (see Non-Patent Document 1). A narrowband CQI is read as channel quality acquired in receiving processing in a mobile station when a base station allocates predetermined subbands, and is used for adaptive modulation of the subbands. Meanwhile, a wideband CQI is read as averaged channel quality acquired in receiving processing in a mobile station when a base station allocates arbitrary subbands, and used for adaptive modulation of arbitrary subbands. FIG. 1 illustrates a narrowband CQI and a wideband CQI. As shown in FIG. 1, the overall system bandwidth is formed with a plurality of RBs. Further, in FIG. 1, a mobile station measures a narrowband (subband) CQI by estimating for example SINR (Signal to Interference plus Noise Ratio), channel quality of two contiguous RBs, and measures a wideband CQI by estimating the channel quality of the overall system bandwidth.
Non-Patent Document 1: 3GPP R1-073681, Nokia Siemens Networks, Nokia, “CQI reporting requirements for E-UTRA UE,” 20-24 Aug. 2007